关于读取txt文件的有关问题

关于读取txt文件的问题。
要把txt文件中的字母abcdefghijklm转换成nopqrstuvwxyz。code 写出来了，但是为什么printout的只有最后一行。
[code=Java][/code]

import java.util.*;
import java.io.*;
public class Rot {

/**
* @param args
*/
public static void main(String[] args)throws IOException {
// TODO Auto-generated method stub
String FileName=readFileName("Please enter an input file name:");
Scanner infile = new Scanner (new File(FileName+".txt"));
String result=transformed(infile);
FileName=readFileName("Please enter an output file name:");
PrintWriter outfile=new PrintWriter(new FileWriter(FileName+".txt"));
System.out.println(result);
outfile.println(result);
infile.close();
outfile.close();
}
public static String readFileName(String msg){
Scanner inkey = new Scanner(System.in);
System.out.println(msg);
return inkey.nextLine();
}
public static String transformed(Scanner in)throws IOException{
String line=null;
int num=13;
while(in.hasNextLine()){
line=in.nextLine();
int count=0;
while(count<line.length()){
char letter=line.charAt(count);
if(letter>='a' && letter<'n')
letter+=num;
else if(letter>='n' && letter<='z')
letter-=num;
if(letter>='A' && letter<'N')
letter+=num;
else if(letter>='N' && letter<='Z')
letter-=num;
count++;
}
}
return line;
}
}

------解决方案--------------------
这就要用到传说中的IO流了。

Java code

public static void main(String[] args) throws IOException {        String dir = "D:/workspace/TestProject/src/com/io/ByteReadFileTest.java";        String src = "D:/workspace/TestProject/src/com/io/out.java";        InputStream input = new FileInputStream(dir);        OutputStream out = new FileOutputStream(src);        int length = 0;        byte[] b = new byte[1024];// 缓冲区        while ((length = input.read(b)) != -1) {            System.out.print(new String(b, 0, length));            out.write(b, 0, length);// 重要...            out.flush();        }        out.close();    }
------解决方案--------------------
while(in.hasNextLine()){ //你每次循环读入一行，进行转换，
line=in.nextLine();      //下一次循环的时候，前一行的信息就丢失了

所以，你应该把每次循环的结果保存到一个临时变量，最后把所有结果返回

即
Java code
StringBuilder buf = new StringBuilder();while(in.hasNextLine()){    line=in.nextLine();    int count=0;    while(count<line.length()){        char letter=line.charAt(count);        if(letter>='a' && letter<'n')            letter+=num;        else if(letter>='n' && letter<='z')            letter-=num;        if(letter>='A' && letter<'N')            letter+=num;        else if(letter>='N' && letter<='Z')            letter-=num;        count++;        buf.append(letter); //保留到临时变量    }    buf.append("\n"); //追加换行符}return buf.toString();